I have been using it lightly. But the biggest problem (for me) is that I cannot use custom icons. I have to use Azure specific icons in a lot of diagrams. Mermaid's support for custom icons is only via iconify packs as far as I can tell. Is it possible to refer to icons in a local directory, such as "./images/storage.png"?

That's good feedback. The icons are not bundled into Mermaid itself due to copyright concerns. The approach you suggest would make sense, though.